1. Field of the Invention
The present invention relates to a puncture sealing agent for a tire, which is prevented from being transformed to a creamy material when being stored for a long term, so as to improve a long-term storability; and a process for producing the same.
2. Description of the Related Art
When a puncture is generated in a tire, a puncture sealing agent is frequently used. The sealing agent is an agent which is poured into the tire to seal up the punctured portion from the inside, thereby ensuring the airtightness of the tire.
As a puncture sealing agent of this type, there is known an agent wherein a rubber latex is blended at least with an adhesive agent and an antifreezing agent. As the antifreezing agent, ethylene glycol is generally adopted.
However, when a puncture sealing agent having such a composition is stored for a long term, rubber particles or adhesive agent particles therein aggregate near the surface so that the sealing agent trends to be transformed to a creamy material. As a result, as illustrated in FIGS. 3A and 3B, this creamy material a closes a taking-out mouth b1 of a container b. Thus, there is caused an inconvenience that an internal sealing agent c cannot be smoothly taken out.
It is presumed that the creamy material a is generated by the following mechanism: in the puncture sealing agent, which is a latex wherein rubber particles and adhesive agent particles are dispersed and floated in an aqueous ethylene glycol solution by ionic repulsive force between the particles and a surfactant, the gravity of the dispersed particles is smaller than that of the aqueous ethylene glycol solution, which is a medium; therefore, the respective rubber particles gradually rise up (float up) in the medium by the action of gravity and the rising particles form a particle-concentrated layer near the surface, whereby the puncture sealing agent is transformed to the creamy material.
Thus, the inventors suggested that instead of ethylene glycol, propylene glycol, which has a smaller gravity than ethylene glycol, was used as an antifreezing agent. According to this invention, the rubber particles come not to rise easily so as to make it possible to suppress the formation of the particle-concentrated layer near the surface.
However, in the case that a puncture sealing agent into which propylene glycol is incorporated at a high concentration is produced, the concentration of a rubber in the rubber latex is high and further propylene glycol is not easily mixed. Therefore, the poured propylene glycol irritates the rubber particles to induce aggregation. For example, a new problem that 5% or more of the whole of the rubber component is generated as aggregation lumps is caused.